Dump vehicles or dump wagons of this type are widely used for agricultural purposes, wherein the vehicle often takes the form of a wagon adapted to be drawn behind a farm tractor. The wagon has a chassis with a frame and wheel structure. A relatively tall sided material holding or dump container is supported on the frame and has a pouring or dump side which is sloped to facilitate discharging of the material out when the container or box is elevated and tilted to the dump position. It is generally desirable that such wagons provide a dumping mechanism so that when the container is in its elevated and tilted position, the pouring edge along one side of the container will be located in a high position to facilitate dumping silage and the like into high sided trucks or storage bins. At the same time, it is desirable that, in the dump position, the pouring edge of the container be located somewhat laterally offset from the chassis to facilitate dumping into a truck or bin which is located alongside.
Prior dump wagons have used a hydraulic cylinder construction to first lift the container by means of an angulated support arm and slide structure to the desired elevated position; once at the end of the travel of the support arm and slide structure the continued action of the lift cylinder tilted the container to its dump position. Such a structure is generally shown in the U.S. Pat. No. 3,844,617 issued Oct. 29, 1974 to Kostman. After the conclusion of the dumping step the lift cylinder is retracted permitting the container to pivot back to its pretilt position and, upon further retraction of the lift cylinder, the container, via the support arm and slide structure, moves down to its original, lowered position.
Because of the size and weight of the container, especially when fully loaded, a lift cylinder and support arm and slide structure are located at each end of the wagon chassis. In order to assure that both ends of the container are raised and lowered uniformly and in unison, an equalizing cable and pulley structure has been used in certain dump wagons. The cable and pulley structure is connected between the support arms at both sides of the container and resists unequal movement of one side relative to the other. This is significant since any canting of the container between the support arm and slide structures could result in wedging and possible damage to these and related structures. During the tilting and dumping action high static and dynamic loads can be imparted to the apparatus which could cause one end of the container to prematurely move down its slide structure relative to the other end whereby wedging could occur. Thus it has been found desirable that each of the support arms be locked in place relative to its slide structure after the container has been elevated to its raised position but before significant tilting has occurred. As noted this is to prevent one side or the other of the container from inadvertently moving back down the slide structure resulting in the undesirable wedging noted.
But there is an additional reason for locking the support arms in position during the tilting and dumping operation. In order to assure that the contents of the container or box have been fully emptied, it is common for the operator to manipulate the hydraulic power to the lift cylinders to rapidly and repetitively pivot the container to and from the fully tilted position to cause the container to oscillate from its fully tilted position. In this way the remainder of the contents of the container can be shaken loose to more completely empty the container. It can be appreciated, however, that this action results in significant vibrational loads being applied to the dump wagon structure. Note that the maximum degree of tilting is controlled by the uppermost, locked position of the support arm and the uppermost position of the lift cylinder. The support arms are located at the pouring side of the container with the container pivotally secured to the upper ends of the arms; the lift cylinders are located adjacent to but offset from the support arms and are connected at the upper end of the container at locations behind the pouring side of the container. Thus the amount of pivoting is controlled by these two location points.
In the past a mechanical lock mechanism located at each end of the container has been used to mechanically lock the support arms in their uppermost locations. Thus the lock mechanism is automatically actuated after the container is in its raised position and begins to be tilted for dumping and is automatically deactuated when the container has been tilted back to its pretilt position. Because of the vibrational and other load factors noted, the mechanical latch at one or both of the support arms could, from time to time, be dislodged whereby one side or both of the container would begin to prematurely move down the slide structure.
At the same time, however, the lift cylinder would be near or at its fully raised position thus placing the container near or at its fully tilted position. However, if the mechanical lock became dislodged, the pouring side of the container could move or slide downwardly along the slide structure; this could result in excessive tilting or overcentering of the container whereby it could no longer be retracted by the lift cylinder. This action could damage the apparatus and/or render it inoperable until the necessary equipment could be secured to move the container back to a position where it can be untilted and lowered. As previously noted, it is also possible that the movement of one side of the container only towards the lowered portion could result in wedging and damage to the apparatus.